Device for flow force compensation

ABSTRACT

A device, consisting of at least one control piston (12) which is longitudinally displaceable in a housing (10) comprising at least two connection points (P, A) for fluid, and which cooperates with a metering edge (34) of the housing (10) at a connection point (P), said point, in control positions of the control piston (12), supplying the other connection point (A) with fluid via a fluid connection, and which piston, as a result of occurring flow forces, tends to be drawn in the direction of a closing position which blocks one of these fluid connections. The device is characterized in that in order to compensate the flow force, the control piston (12) has, in the region of the control edge (34) of the housing (10), a shape modification (48) of its cylindrical exterior basic form (50), such that a flow contact surface (52) for fluid is created, which surface transfers a compensating force that acts against the flow force to the control piston (12) and that seeks to pull the control piston (12) into an opening position opposed to the closing position.

The invention relates to a device consisting of at least one regulating piston, which is guided longitudinally movably in a housing having at least two ports for fluid, and which interacts with a control edge of the housing at a port, which supplies the other port with fluid in regulating positions of the regulating piston via a fluid connection while aiming at pulling [the piston] in the direction of a closing position blocking this fluid connection due to occurring flow forces.

From DE 10 2014 004 796 A1 a proportional pressure regulating valve is known having a generic device having a longitudinally movable regulating piston guided in a valve housing, which piston is used to selectively connect ports present in the valve housing, such as a

-   -   pressure supply port (P),     -   load port (A) and     -   tank port or return port (T),         by means of a solenoid operating system, wherein a first         characteristic curve is established between a control signal of         the solenoid operating system and the flow volume or the         actuating pressure (P), in relation to a load, which can be         connected to the load port (A). In this known solution, a         control device is used to generate a second characteristic         curve, which differs from the first characteristic curve, for         the load, which can be connected to the load port (A) of the         valve housing, after having passed through the first         characteristic curve. As a result, a different valve behavior is         achieved for pre-definable applications of the known pressure         regulating valve, in turn increasing the range of applications         for this proportional pressure control valve.

So-called flow forces act on this regulating process, due to the existing pressures and the volume flows to be managed at the ports, acting on the valve piston or regulating piston of the device, wherein these flow forces are regularly caused by a pressure drop at the assignable control edge or regulating edge in the housing, for example, in the range of a pump supply connection or pressure supply connection (P) for the load port (A), wherein this pressure drop causes a force in the direction of the device connected to the solenoid operating system, which aims at moving the regulating piston in the direction of its closed position, which further reduces the pre-defined pressure.

For certain applications, such as in coupling applications, however, a quick “filling” of the coupling is necessary for their targeted operation, i.e. controlled valves of this type are generally not particularly suitable. This can be remedied by the use of so-called pilot operated valves (DE 10 2012 015 356 A1), these valves show an increased leakage due to the pilot oil flowing toward the tank or return, however, resulting in increased power losses. Another option is increasing the magnetic force of the solenoid operating system, which increases the space requirement and results in increased costs both in the production and in the operation of the valve.

Based on this prior art, the present invention addresses the problem of providing a device which is particularly suitable to be used in pressure regulating proportional valves and does not have the disadvantages described above and can be produced and operated inexpensively and is of compact design. A device having the features of claim 1 in its entirety solves this problem.

Because, according to the characterizing part, the regulating piston changes its shape from its basic outer cylindrical shape in the area of the control edge of the housing, for a flow force compensation such that an effective flow surface for fluid is created, which causes a compensating force on the regulating piston against the flow force, which aims at pulling the regulating piston into an open position opposite to the locking position, a counterforce to the flow force is generated in the operation of the device according to the force formula F=P×A.

As the control edge or regulating edge is “shifted” and the fluid pressure on the change in shape in the form of a circular ring on the regulating piston as a compensation surface regularly remains constant, the flow force still acts in the direction of the solenoid operating system, but at the same time the newly generated counterforce acts as flow force compensation on the regulating piston via the surface or change in shape in the direction of one of the ports in the housing, in particular in the form of a load port. In this way it is possible to reduce the flow forces occurring during the operation of the device or the valve in a structurally simple and cost-effective manner. Advantageously, in the device according to the invention, therefore, the inlet pressure is used to compensate the flow force. The pressure level occurring there is generally higher than that on the return side of the device, such that larger volume flows can be more easily managed in a regulating manner. Advantageously, the fluid flowing through the device is deflected by 90° in the area of the control edge or regulating edge and the change in shape in the regulating piston such that the fluid impulse occurring can rest against the whole area of the change in shape or the compensating surface thus created.

If the device according to the invention is used in an advantageous manner for a directly controlled valve, the flow force compensation produced in this way permits the use of smaller solenoid operating systems, which regularly show an improved, prompt actuation behavior.

Further advantageous embodiments of the solution according to the invention are the subject of the other dependent claims.

Below, the device according to the invention will be presented in more detail based on an application for a 3-way pressure control proportional valve. In the schematic figures, which are not to scale,

FIG. 1 shows a longitudinal section through the essential components of the aforementioned proportional valve;

FIGS. 2 and 3 show a device known in the prior art or the compensation device according to the invention in an enlarged view of a circular image detail denoted by X in FIG. 1.

FIGS. 4 and 5 show pressure regulating characteristics of the prior art and the characteristics, which are achieved using the device for flow force compensation or force control.

FIG. 1 shows a longitudinal section of a known 3-way proportional pressure control valve having a longitudinally movable regulating piston 12 guided in a valve housing 10, which piston is used to selectively connect ports, such as a pressure supply or pump port P, a load port A, and a tank port or return port T, present in the valve housing 10, by means of an operating system in its entirety designated by 14. The operating system 14 shown in FIG. 1 is formed like a solenoid; but operation by means of a pneumatic or other fluidic actuator (not shown) would also be feasible. Also, a mechanical operating system for the regulating piston 12 is not excluded in principle.

The solenoid 14 has a coil winding 16 in a coil body 18 as customary and therefore not described in greater detail, wherein the coil winding 16 of the operating coil can be supplied with a control current via a connector part 20. In the direction of the valve housing 10, the coil body 18 adjoins a pole plate 22, the free end face of which is encompassed by a flange plate 24, which is to mount the pressure regulating valve to a valve block, not shown. In that way the pressure regulating valve shown in FIG. 1 can be mounted in the valve block (not shown) in the manner of a cartridge insert or in the manner of an insert cartridge, which valve block has matching connection geometries, which may be brought into fluid-conducting alignment with the aforementioned ports P, A and T in the valve housing 10. The valve shown does not have a 100% pole tube. The control edge is formed onto the anchor plate 22. Furthermore, there is a separate sleeve, which seals the fluid chamber.

A magnet armature 26, which has a pressure equalization channel 28, is guided longitudinally movably in the coil body 18 to allow an obstacle-free reciprocating motion of the armature 26 in the solenoid in a pressure-balanced manner. Viewed in the direction of FIG. 1, the cylindrical magnet armature 26 has an operating rod 30 on its right free end side, which rod permanently rests against the regulating piston 12. For this purpose, the right end of the regulating piston 12, viewed in the direction of FIG. 1, is held in permanent contact with the operating rod 30 by an energy store in the form of a compression spring 32, wherein the compression spring 32 aims to bring the regulating piston 12 in a left stop position in the form of a stop 33 at the left inside of the valve housing 10.

In the displacement position of the regulating piston 12 shown in FIG. 1, the latter controls a control edge or regulating edge 34 at the valve housing 10 and regulates the feasible fluid flow from port P to port A via the fluid chamber 36 of the regulating piston 12 which is designed as a hollow piston. If the solenoid is 14 energized further, the regulating piston 12 moves further to the right in the direction shown in FIG. 1 against the action of the compression spring 32 and the opening or regulating cross section at the control edge or regulating edge 34 mentioned is opened further, such that fluid volume from the pressure supply port or pump terminal P increasingly flows to the load port A, which is introduced into the front side of the valve housing 10 and has a permanently fluid-conveying connection to the fluid chamber 36 of the regulating piston 12. If the solenoid 14 remains de-energized, the compression spring 32 shifts the arrangement consisting of regulating piston 12, operating rod 30 and magnet armature 26, as viewed in the direction of FIG. 1, to the left, at most until the regulating piston 12 comes into contact with the stop 33 of the valve housing 10.

In the pertinent position of the regulating piston 12, the load port A is connected to the tank or return port T via a groove 38 in the regulating piston 12 in a fluid-conveying manner, which groove is permanently connected to the fluid chamber 36 in a fluid-conveying manner and the axial length of which is smaller than the length of the inner wall area of the valve housing 10 between the port P and the port T. In this position, the pressure supply port P is disconnected from the load port A because the regulating piston 12 has passed over the control edge or regulating edge 34; a displacement position, as is apparent from FIG. 2 in the prior art. To form the pressure supply port or pump port P and the tank port or return port T, rows of drilled holes 40 and 42 are introduced into the valve housing in a conventional manner, wherein FIGS. 2 and 3 show a part of a drilled hole of the row of drilled holes 40. To permit the regulating piston 12 to move without obstruction in the valve housing 10, a throttle channel 44 is introduced at the left end side, which extends between the interior of the valve housing 10 having the stop 33 and the fluid chamber 36 in the interior of the hollow-bore regulating piston 12 through the end wall thereof.

In the de-energized state, therefore, the pressure supply or pump port P is closed and the load port A is connected to the tank port or return port T. If a current signal is then applied to the coil winding 16 of the solenoid 14 via the connector part 20, the solenoid 14 presses on the regulating piston 12 in the direction of the load connection A with a force corresponding to the magnitude of the control current. As a result, the regulating piston 12 is moved to the right against the return spring 32 and the fluid (oil) flows from the pressure supply port or pump port P to the load port A. Depending on the type of load, not shown, for example in the form of a motor vehicle clutch, a counter pressure then builds up at the load port A, which acts on the surface of the regulating piston at the valve and generates a counterforce to the magnetic force of the solenoid, which moves the regulating piston 12 back into the opposite direction of control. In this way, the inflow from the pressure supply or pump connection P to the load port A is reduced until the pressure applied to the load port A corresponds to the magnetic force and thus to the pressure value specification based on the current signal.

If the load now no longer requires pressurized fluid, as is the case when the clutch is at the stop, the cylindrical regulating piston 12 moves further back and closes the drilled inlet holes 40 of the pressure supply or pump port P as shown in the prior art FIG. 2 and interrupts the fluid supply to the load port A to that extent. If the output pressure drops below the setpoint pressure due to the depressurization of the connected load, the armature 26 uses the operating rod 30 to push the regulating piston 12 back towards the right and the control process restarts. The magnetic force of the solenoid 14 defines the maximum attainable regulating pressure. If the pressure at the load port A rises above the preset value, the magnet armature 26 pushes the regulating piston 12 to the left viewed in the direction of FIG. 1 and opens the connections from the load port A to the return port or tank port T. In this way the pressure at the load port A is limited.

Owing to pressure flow and volume flow acting on the regulating piston 12, so-called flow forces also act on this regulating process. These flow forces cause a pressure drop at the control edge or regulating edge 34 (cf. FIG. 2), this pressure drop creates a force in the direction of the solenoid 14, wherein the regulating piston 12 is moved in the direction of its closed position, i.e. to the left viewed in the direction of FIG. 1. Thereby the pre-defined pressure is further reduced because the known valve solution according to FIG. 2 moves into its closed position. The resultant characteristic can be seen in FIG. 4 detailing the prior art. The characteristic field framed by an ellipse 46 for emphasis shows how the known pressure regulator behaves with increasing volume flow. If, for example, the volume flow is increased to 5 I per minute at 4 bar, the pressure drops to zero bar. Because, as mentioned, in coupling applications for the valve above, the coupling has to be “filled” quickly, this known valve would not be suitable for such an application, as the closing behavior of the valve specifically prevents the rapid filling of the coupling.

This is where the invention comes in, which generates a counterforce to the flow force due to its structural design, which will be explained in more detail below, in particular with reference to the illustration of FIG. 3 and FIG. 5.

As is apparent in particular from the illustration according to FIG. 3, the regulating piston 12 shows a change in shape 48 from its cylindrical outer basic shape 50 for a flow force compensation in the region of the control edge or regulating edge 34 of the housing 10. Due to this change in shape 48, an effective flow surface 52 for fluid is provided, which causes a compensating force on the regulating piston 12 counteracting the flow force, which compensating force aims at pulling the regulating piston 12 into an open position opposite to the locked position; i.e. viewed in the direction of looking at FIG. 1 from the left to the right. The effective flow surface 52 is perpendicular to the longitudinal or travel axis 54 of the regulating piston 12 and can be moved conjointly with the latter.

The change in shape 48 consists in particular of a discontinuity in diameter, preferably of an offset 56 in the regulating piston 12, which is set back from a free end face 58 of the regulating piston 12 in the region of its groove 38 away from the latter in the direction of the port A. The effective flow surface 52 forms an annular surface and is arranged in abutment with the control edge or regulating edge 34 in a regulating position of the housing 19 or in its extension, wherein the fluid connection between the two ports P, A is actuated.

The change in shape 48 in the regulating piston 12 forms an annular fluid control chamber 60, which during regulating operation is subject to a lower fluid pressure on the return side 62 of the device than the pressure present at the port P in the valve housing 10, wherein the respective pressures to be actuated are greater than the tank pressure or the ambient pressure.

As can be further seen from the illustration according to FIG. 3, when the fluid cross section is opened, i.e. when the regulating piston 12 is moving to the right, a fluid diversion of approximately 90° is effected in operation such that the resulting impulse can rest against the entire effective flow surface 52 in the direction of the terminal A, wherein the change in shape 48 is then exposed to a constant fluid pressure during the regulating process.

According to the invention, the discontinuity in diameter in the form of the step 56 is formed by two different diameters in the regulating piston 12, the smaller diameter opening into the recess or channel 38 in the regulating piston 12 mentioned above.

To compensate for the flow force by a counterforce, a surface 52 has been added to the regulating piston 12, below the control edge or regulating edge 34. In this arrangement the input pressure at the pump port or pressure supply port P can be used to compensate for the flow force. The surface 52 at the port P can be used to generate the counterforce to the flow force according to the force formula F=P×A. Because the control edge or regulating edge 34 is “shifted” in this way but the pressure on the annulus 52 remains constant, the flow force continues to act in the direction of the solenoid 14, the newly generated counterforce [acts] via the surface 52 at the regulating piston 12 in the direction of load port A, however. Thus, while the flow force tries to pull the regulating piston 12 in a closed position, the counterforce generated counteracts by moving or pulling the regulating piston 12 to an opening position. The associated horizontal pressure characteristic curve is reproduced in FIG. 5 for a range, which is bordered by an ellipse 64 for clarification. This results in a largely harmonious filling behavior for a load connected to the load port A, such as a motor vehicle clutch.

The device according to the invention does not need to be limited to applications using direct-controlled compact pressure regulators, such as the proposed valve. Such a flow force management in the way of compensation can also be easily implemented using slide valves. Furthermore, two ports, which are to be connected to each other in a fluid-conveying manner in a regulating manner, are sufficient to be able to perform the flow-force compensation in the frame outlined. In that regard, the device according to the invention can basically be applied anywhere where ports are to be connected to each other and separated again in a regulatory manner in a fluid-conveying manner via a regulating piston. In particular, by using the flow force compensation according to the invention, solenoids can be built more compactly, which improves the actuation behavior and helps to save costs and installation space. This is without parallel in the prior art. 

1. A device comprising at least one regulating piston (12), which is guided longitudinally movably in a housing (10) having at least two ports (P, A) for fluid, and interacting with a control edge (34) of the housing (10) at a port (P), which supplies the other port (A) in regulating positions of the regulating piston (12) with fluid via a fluid connection and thereby aims at pulling [the piston] towards a closed position blocking this fluid connection due to occurring flow forces, characterized in that the regulating piston (12) shows a change in shape (48) from its basically cylindrical outer shape (50) in the area of the control edge (34) of the housing (10) for a flow force compensation such that an effective flow surface (52) for fluid is provided, which causes a compensating force acting against the flow force to be introduced into the regulating piston (12), which force aims at pulling the regulating piston (12) into an opening position opposite to the blocked position.
 2. The device according to claim 1, characterized in that the regulating piston (12) can be actuated by a magnet armature (26) of a solenoid (14), which in the energized state aims at moving the regulating piston (12) against the action of an energy storage device (32) in the direction of regulating positions in which it opens the fluid connection between the two ports (P, A), and that in the event that a counter pressure acting on the regulating piston surface builds up on the load port (A), and generates a counterforce to the magnetic force of the solenoid (14), the regulating piston (12) is moved back into an opposite direction of control, in which the inflow from the pressure supply port (P) to the load port (A) is reduced until the pressure applied to the load port (A) corresponds to the magnetic force and thus to the pressure value specification by the current signal of the solenoid (14).
 3. The device according to claim 1, characterized in that the change in shape (48) in the regulating piston (12) forms an annular fluid control chamber (60), which during regulating operation is subject to a lower fluid pressure on the return side (62) of the device than the pressure prevailing at the port (P) in the valve housing (10), and that the pressures to be actuated are greater than the tank pressure or the ambient pressure.
 4. The device according to claim 1, characterized in that the control edge (34) of the housing (10) with the change in shape (48) of the regulating piston (12) causes a fluid bypass of 90° in operation, such that the resulting pulse rests against the entire effective flow surface (52) and the change in shape (48) is subject to a constant fluid pressure.
 5. The device according to claim 1, characterized in that the discontinuity in diameter is formed by two different diameters in the regulating piston (12) and that the smaller diameter opens at least partially into a recess (38) of the regulating piston (12).
 6. The device according to claim 1, characterized in that in the traversing position of the regulating piston (12), in which the bottom of the discontinuity in diameter is in annular contact with the control edge (34), which is bounded by the one port (P), the smaller diameter of the discontinuity in diameter of the regulating piston (12) is kept free of further ports arranged in the vicinity and which immerses in a receiving space thereof a radial distance from the housing (10).
 7. The device according to claim 1, characterized in that it is part of a 3-way pressure control proportional valve, which is preferably directly controlled in the valve housing and also has a further port (T).
 8. The device according to claim 1, characterized in that in the de-energized state of the solenoid (14), the regulating piston (12) travels in the housing (10) to the stop (33) and thereby creates the fluid connection between the further port (T) and one (A) of the two other ports (P, A), which can be connected to a hydraulic load, and that the remaining port (P) is closed by the regulating piston (12).
 9. The device according to claim 1, characterized in that the solenoid (14) can also be used to actuate the fluid connection to the port (T) leading to the pressure sink.
 10. The device according to claim 1, characterized in that the ports (P, T) are introduced radially into the housing (10) and the port (A) engages axially into the valve housing (10) from the free end side thereof.
 11. The device according to claim 1, characterized in that the regulating piston (12) is designed as a hollow piston and in that the recess (38) in the regulating piston (12), preferably in the form of at least two pockets extending through the housing (10), as viewed in the axial direction is shorter than the distance between the port (P), which can be connected to a pressure supply source, and the port (T), which can be connected to the pressure sink. 